The invention relates to a fuel tank made of plastic for motor vehicles, wherein an insert enclosing a space is located in the interior of the fuel tank. The wall of the fuel tank may consist of a single blow-molded piece having a sufficiently large opening or of two pressed or deep-drawn plastic shells which are subsequently joined together. The mentioned shaping processes use a mold, wherein the plastic is molded at a warm state. The walls may also be multilayered in order to minimize permeation of fuel vapors. The insert may be of different kinds; usually it is part of a venting system, such as a separator, a debubbling tank and/or a float chamber.
In the case of conventional fuel tanks made of plastic, the parts of the venting system are individually mounted at the inside of the upper shell either by welding (see, for example, EP 1 310 715 A1) or by attaching them to weld crowns secured in through-holes of the shell (see, for example, EP 1 084 889 A1).
U.S. Pat. No. 4,531,653 discloses a block-shaped fuel tank made of sheet metal, wherein a stack of three rectangular profiled metal sheets is welded to the inside of the planar top wall of the block-shaped fuel tank. These metal sheets are welded together to form a rigid body extending horizontally over the whole base area of the fuel tank. The rigid body defines chambers connected to one another and to the interior of the fuel tank and the atmosphere, respectively. This design is complex and only applicable in the case of a planar top wall made of sheet metal. And even then its durability remains questionable because of the tolerances and because of residual stresses caused by the welding process.
EP 1 213 173 discloses a fuel tank made of plastic, wherein a body defining a closed space, which is therein referred to as an evaporator unit, is fixed by screws to the inside of the top wall of the fuel tank. For this purpose, the wall is provided with undercut support parts, rendering its manufacture difficult and expensive. Also, the body fixed by screws is a likewise complicated part; on top of that, its assembly is very complex.
Finally, US 2008/014 96 42 A1 discloses a fuel tank made of thermoplastic material comprising installation parts which are welded thereto in the first heat when the tank is shaped. In order to achieve that the finished article cools down evenly and without shrinkage distortion by a subsequent gas flushing process, the installation part is connected to the tank wall in such a way that it defines a separate volume together with the tank wall. This volume can be a channel or a surge container arranged at the bottom of the tank. Further applications are not envisaged.
Thus it is the object underlying the invention to form the insert of a fuel tank made of plastic such that great economy of space and design flexibility is achieved, while the wall of the fuel tank and the insert have simple shapes and the assembly of the insert is as easy as possible. This insert is also to be suitable for fuel tanks with top walls having a non-planar spatial shape due to installation conditions in the vehicle.